I. Field
The following description relates generally to wireless networks, for example radio resource connection (RRC) in wireless communication systems, such as E-UTRAN.
II. Background
Wireless communication networks are commonly used to communicate information regardless of where a user is located and whether a user is stationary or moving. Generally, wireless communication networks are established through a mobile device (or “access terminal”) communicating with a series of base stations (or “access points”).
Typically, as an access terminal moves from one location serviced by a first access point to a second location serviced by a second access point, a communication “handoff” will be performed such that the access terminal stops communication via the first access point and starts communicating via the second access point. While seemingly simple in concept, such handoffs are often very complex and wrought with problems. For instance, if the two access points in the example above are not synchronized, then the access terminal may have trouble determining if the second access point exists and/or determining critical information that would allow the access terminal to recognize and start communicating with the second access point.
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP LTE systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{/NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
For FDMA based systems, two kinds of scheduling techniques are typically employed, including: (1) Subband Scheduling where user packets can be mapped to tone allocations confined to a narrow bandwidth and may be referred to as frequency selective scheduling (FSS) in this disclosure; and (2) Diversity Scheduling where user packets are mapped to tone allocations spanning an entire system bandwidth and may be referred to as frequency hopped scheduling (FHS) in this disclosure.
Frequency Hopping is typically employed to achieve both channel and interference diversity. From that perspective, frequency hopping within a subband may also be performed with FSS.
In a given system, however, all users may or may not always benefit from FSS. Accordingly, it may be beneficial to employ advantageous design hopping structures such that FSS and FHS users can be easily multiplexed within the same Transmission Time Interval (TTI). Thus, new technologies directed to improving handoffs between cellular devices may be useful.